Pipe Schedule Dimensions

Pipe schedule is a dimensionless number that relates to the wall thickness of a pipe for a given nominal pipe size (NPS). Higher schedule numbers mean thicker walls and higher pressure ratings. Common schedules include Sch 5, 10, 40, 80, and 160. Schedule 40 is the most common for general industrial use in carbon steel.

NPS (Nominal Pipe Size) is a label, not a measurement. For NPS 1/8 through NPS 12, the outside diameter (OD) does not equal the NPS value — for example, NPS 2 pipe has an OD of 2.375 inches. For NPS 14 and larger, the OD equals the NPS value in inches. The OD stays constant across all schedules for a given NPS; only the wall thickness (and therefore ID) changes.

For low-pressure steam (up to 15 psig), Schedule 40 carbon steel is typical. Medium-pressure steam (15-150 psig) often uses Schedule 40 or 80. High-pressure steam (above 150 psig) may require Schedule 80, 120, or 160 depending on temperature and pressure. Always verify against ASME B31.1 (power piping) or B31.3 (process piping) minimum wall thickness calculations for your specific conditions.

Carbon steel pipe follows ASME B36.10 and includes schedules from 5 through 160 plus standard (Std), extra strong (XS), and double extra strong (XXS). Stainless steel pipe follows ASME B36.19 and uses schedules 5S, 10S, 40S, and 80S. The 'S' schedules have the same OD as carbon steel but may have different wall thicknesses. For sizes NPS 12 and below, Sch 40S equals Sch 40.

DN (Diametre Nominal) is the metric designation that corresponds to NPS. The conversion is not a direct unit conversion — DN 50 corresponds to NPS 2, not 50 mm. Common equivalents: DN 15 = NPS 1/2, DN 25 = NPS 1, DN 50 = NPS 2, DN 100 = NPS 4, DN 200 = NPS 8, DN 300 = NPS 12. This table shows both NPS and DN values for reference.

EN 10220 is the European/metric standard for steel pipe outside diameters; ASME B36.10 is the North American standard. Most common sizes overlap (DN 50 = NPS 2 = OD 60.3 mm), but some don't — for example DN 125 (OD 139.7 mm) has no exact NPS equivalent (NPS 5 is 141.3 mm), and DN 600 (610.0 mm) is slightly larger than NPS 24 (609.6 mm). EN pipe is also specified by wall thickness in millimeters from EN 10216-1 (seamless) or EN 10217-1 (welded), rather than by schedule number. The EN 10220 entries in this table use the legacy DIN 2448 standard wall thickness for each DN — what most European suppliers carry as default stock.

ASTM B88 (Type K, L, M) is the North American copper water tube standard, with imperial-based OD progression (e.g. NPS 1/2 has OD 0.625 in / 15.9 mm) and three wall thicknesses. EN 1057 is the European copper tube standard for water and gas, using metric OD designations directly — a '22 mm tube' is 22.0 mm OD exactly. EN 1057 covers OD 6 mm to 267 mm and is used throughout EU plumbing, HVAC, and industrial water systems. The two standards are not interchangeable: EN 22 mm ≠ ASTM 3/4 in (which is 19.05 mm OD).

EN 10220 (formerly DIN 2448) is the general-purpose European standard for steel pipe outside diameters, covering DN 6 to DN 2200 and intended for any steel pipe application — process, structural, mechanical. EN 10255 (formerly DIN 2440 / DIN 2441) is specifically for non-alloy steel tubes suitable for welding and threading, used in water, gas, low-pressure steam, and fire-protection systems. EN 10255 covers DN 6 to DN 150 and is published in three thickness series: L (light), M (medium / DIN 2440 successor), and H (heavy / DIN 2441 successor). Most ODs are identical to EN 10220 but DN 150 differs: EN 10255 uses 165.1 mm while EN 10220 uses 168.3 mm. If your project specifies threaded connections or matches DIN 2440 historical practice, use EN 10255.

Both standards specify HDPE pipe by SDR (Standard Dimension Ratio = OD ÷ wall), but use different OD progressions. ASTM D3035 follows the IPS (Iron Pipe Size) system shared with steel pipe — DN 100 HDPE has OD 4.5 in / 114.3 mm, matching NPS 4 carbon steel. EN 12201 / ISO 4427 follows a metric progression (20, 25, 32, 40, 50, 63, 75, 90, 110, 125, 140, 160, 180, 200, 225, 250, 280, 315 mm…) that doesn't match ASME steel sizes. EN 12201 is the dominant standard for water-supply HDPE in Europe and increasingly worldwide. Pipe is rated by both SDR and PN (nominal pressure in bar) — for PE 100 material: SDR 11 = PN 16, SDR 17 = PN 10, SDR 26 = PN 6.